Question

The semiconductor elements like silicon and germanium are usually purified by:
A.Distillation
B.Zone-refining
C.Liquidation
D.Electrolytic refining

Answer 1

Semiconductors are materials that have electrical conductivity value between that of the conductors such as metals and insulators such as glass. Unlike the conductors, their resistivity falls as the temperature rises.

Complete answer:
The Semiconductor elements like silicon and germanium are usually purified by the method of “Zone-refining” which is also known as “zone-melting”, “floating-zone process”, and “travelling melting zone”. These are a group of similar methods used for purifying crystals in which a narrow region of a crystal is melted and this molten zone is moved along with the crystal. The molten region melts impure solid at its forward edge and leaves a wave of pure material solidified behind it as it moves through the ingot. The impurities concentrate in the melt are moved to an end of the ingot. This method was developed by John Desmond Bernal and William Gardener Pfann in Bell labs as a method to prepare high purity materials, mainly semiconductors for manufacturing transistors.

Hence, the correct option is option B.

Note:
A process that is similar to zone-refining is the “Zone-Remelting” I which two solutes are distributed throughout a pure metal. This is important in the manufacture of semiconductors where two solutes of opposite conductivity are used. For example, in germanium pentavalent elements of group 15 such as antimony and arsenic produce negative for n-type conduction and trivalent elements of group 13 like aluminium and boron produce positive or p-type conduction.